(1) Field of the Invention
This invention relates to metallic seals, and more particularly to bellows seals.
(2) Description of the Related Art
A variety of metallic seal configurations exist. Key metallic seals are commonly held under compression between two opposed flanges of the elements being sealed to each other. Such metallic seals may be used in a variety of industrial applications.
Key examples of such metallic seals are of an annular configuration, having a convoluted radial section which permits the seal to act as a spring and maintain engagement with the flanges despite changes or variations in the flange separation. Certain such seals have an S-like section while others have a section similar to the Greek letter ε with diverging base and top portions. Other similar seals are formed with additional convolutions. One exemplary seal is sold by The Advanced Products Company, North Haven, Conn., as the E-RING seal. Such seals are commonly formed as a monolithic piece of stainless steel or superalloy. Such seals are commonly formed from sheet stock into a shape that is effective to provide the seal with a desired range of compressibility from a relaxed condition.
A particular application where a bellows seal cannot easily be used is in horizontally split gas turbine engines. Horizontally split gas turbine engines are formed in two halves and have a lower casing and an upper casing that can be bolted together once the rotating shaft and other components have been installed. Brush seals are well known to those skilled in the art and are used to provide a fluid-tight seal between a high-pressure region of the engine and a low-pressure region of the engine. Brush seals usually include an annular head portion that is coaxial with the shaft. A plurality of bristles extend from the head portion towards the shaft such that the ends of the bristles wipe against the surface of the shaft. For assembly purposes, a brush seal is normally formed from four separate brush seal segments each having ninety degrees of arc. To prevent bypass leakage from the high-pressure region of the engine to the low-pressure region of the engine the brush seals are normally made a tight fit in a groove provided in the lower and upper casings. This makes removal of the brush seals very difficult and leakage between the head portion and the groove is not well controlled. However, the specific construction of horizontally split gas turbines engines is such that it not possible to split the lower and upper casings vertically around the brush seal. This means that a spring seal cannot be used because it would have to be compressed before it could be inserted into a sealing channel provided between the head portion of the brush seal and a wall of the groove provided in the lower and upper casing.